Food companies prefer studies of single nutrients because they can use the results to sell products. Add vitamins to candies, and you can market them as health foods. Health claims on the labels of junk foods distract consumers from their caloric content. This practice matters because when it comes to obesity—which dominates nutrition problems even in some of the poorest countries of the world—it is the calories that count. Obesity arises when people consume significantly more calories than they expend in physical activity.

America’s obesity rates began to rise sharply in the early 1980s. Sociologists often attribute the “calories in” side of this trend to the demands of an overworked population for convenience foods—prepared, packaged products and restaurant meals that usually contain more calories than home-cooked meals.

But other social forces also promoted the calorie imbalance. The arrival of the Reagan administration in 1980 increased the pace of industry deregulation, removing controls on agricultural production and encouraging farmers to grow more food. Calories available per capita in the national food supply (that produced by American farmers, plus imports, less exports) rose from 3,200 a day in 1980 to 3,900 a day two decades later.

The early 1980s also marked the advent of the “shareholder value movement” on Wall Street. Stockholder demands for higher short-term returns on investments forced food companies to expand sales in a marketplace that already contained excessive calories. Food companies responded by seeking new sales and marketing opportunities. They encouraged formerly shunned practices that eventually changed social norms, such as frequent between-meal snacking, eating in book and clothing stores, and serving larger portions. The industry continued to sponsor organizations and journals that focus on nutrition-related subjects and intensiﬁed its efforts to lobby government for favorable dietary advice. Then and now food lobbies have promoted positive interpretations of scientiﬁc studies, sponsored research that can be used as a basis for health claims, and attacked critics, myself among them, as proponents of “junk science.” If anything, such activities only add to public confusion.

Marion Nestle is Paulette Goddard Professor in the department of nutrition, food studies and public health and professor of sociology at New York University. She received a Ph.D. in molecular biology and an M.P.H. in public health nutrition from the University of California, Berkeley. Nestle’s research focuses on scientiﬁc and social factors that inﬂuence food choices and recommendations. She is author of Food Politics (2002, revised 2007), Safe Food (2003) and What to Eat (2006). She also writes a popular nutrition blog, Food Politics.